Paper-based flexible laminates tendency to curl

144 Pages·2017·4.13 MB·English

by  Erik Andersson

Paper-based flexible

laminates tendency to curl
Clémentine Muller
DIVISION OF PACKAGING LOGISTICS | DEPARTMENT OF DESIGN SCIENCES
FACULTY OF ENGINEERING LTH | LUND UNIVERSITY
2018

MASTER THESIS
This Master’s thesis has been done within the Joint European
Master Course FIPDes, Food Innovation and Product Design.
Paper-based flexible
laminates tendency to curl
Investigating the effect of humidity and temperature

Clémentine Muller
Paper-based flexible laminates tendency to curl
Investigating the effect of humidity and temperature

Copyright © 2018 Clémentine Muller

Published by
Division of Packaging Logistics
Department of Design Sciences
Faculty of Engineering LTH, Lund University
P.O. Box 118, SE-221 00 Lund, Sweden

Subject: Food Packaging Design (MTTM01)
Division: Packaging Logistics
Supervisor: Daniel Hellström
Examiner: Klas Hjort

This Master´s thesis has been done within the Joint European Master Course
FIPDes, Food Innovation and Product Design.

www.fipdes.eu

ISBN 978-91-7753-752-6
Table of contents
Abstract 1
Executive summary 3
Acknowledgments 9
List of acronyms and abbreviations 11
1 Introduction 13
1.1 Background 13
1.2 Research problem 14
1.3 Purpose and aims 15
1.4 Focus and demarcation 15
2 Literature review 17
2.1 The “flexible” packaging industry 17
A growing demand for flexible plastic packaging solutions 18
The nature of flexible laminates 20
2.2 Paper-based laminates materials properties 21
Paper 21
Aluminium foil and metallized films 23
Heat sealing agents 24
Adhesives 24
Primers 26
Other miscellaneous coatings 27
2.3 Paper-based laminates manufacturing processes 27
Adhesive lamination 27
Extrusion lamination 29
Hot-melt lamination 30
2.4 Paper-based laminates curl phenomenon 31
Framework of factors leading to the curl phenomenon 32
Relative humidity 33
Past moisture history 34
Temperature 35
Practices to avoid paper curl 36
3 Materials and method 39
3.1 Packaging materials 39
3.2 Test method to assess the tendency to curl 41
3.3 Environmental conditions to be studied 44
3.4 Experimental design 48
Sampling technique 48
Samples pre-conditioning 49
Samples exposure duration 49
Experimental procedure 50
Experimental plan 54
4 Results and discussion 57
4.1 Case of the Pap/mPET/HSL laminate 57
Effect of the pre-conditioning phase 57
Effect of relative humidity and temperature on curl 58
Effect of PE wrapping 66
Conclusions from the analysis of the laminate tendency to curl 68
4.2 Case of the Alu/Pap/PE laminate 69
Understanding the recommendations made in the DIN 55403 standard as
regard to the cross-cut test method 69
Effect of the pre-conditioning step 72
Effect of relative humidity and temperature 72
Effect of PE wrapping 74
Conclusions from the analysis of the laminate tendency to curl 77
5 Conclusions and recommendations 79
5.1 Conclusions 79
Main factors leading to paper-based flexible laminates curl 79
Impact of relative humidity and temperature on the selected
Pap/mPET/HSL and Alu/Pap/PE laminates behaviour 79
Materials climate-related risk assessment 80
Solution to reduce paper-based laminates tendency to curl 81
5.2 Further research recommendations 81
Limitations of the study 81
Future research suggestions 82
References 85
Appendix A Additional data 95
A.1 Test method selection 95
A.1.1 Comparison of the three test methods 95
A.1.2 Round sample method 96
A.1.3 Determination of the flatness temperature 97
A.2 Pap/mPET/HSL laminate 98
A.2.1 Raw data 98
A.2.2 Overall laminate tendency to curl 113
A.3 Alu/Pap/PE laminate 114
A.3.1 Raw data 114
A.3.2 Overall laminate tendency to curl 132
A.3.3 Predict curl as a function of climate chamber and room conditions 133

Abstract
The main purpose of this study is to assess the impact of environmental conditions
on paper-based flexible laminates tendency to curl. Any deviation in flatness may
indeed affect materials processability. Two different paper-based flexible laminates
are considered: a widely processed heat-sealable yogurt lid (paper / metallized
polyethylene terephthalate / heat-sealing lacquer) and a prototype laminate
(aluminium / paper / polyethylene). Packaging materials sheets (54*36 cm) are
namely sampled from packaging materials rolls. Their tendency to curl is assessed
by implementing the cross-cut method described in the German DIN 55403 standard
(Deutsches Institut für Normung (DIN), 2014). Fifteen climates are tested i.e. five
different relative humidity values (30%, 40%, 50%, 60% and 70%) and three
different temperature values (20°C, 25°C and 30°C). The effect of a polyethylene
wrapping is also evaluated as a potential solution to prevent or reduce curl. For the
yogurt lid which is shown to be sensitive to climate conditions, deformation occurs
in both machine and cross-machine directions: average curl values respectively
reach 13 millimetres and 37 millimetres. An equation to predict curl parameters as
a function of climate and room conditions is furthermore suggested (r² = 72%).
For the prototype laminate which appears not to be sensitive to climate conditions,
deformation happens to be much lower than for the first material and only occurs in
the machine direction. Average curl values reach 3 millimetres in the machine
direction and zero millimetres in the cross-machine direction. Finally, considering
the material-specific results obtained for the two laminates, no general conclusion
can be drawn as regard to the polyethylene wrapping effect.

Keywords: flexible laminates, paper, curl, relative humidity, temperature.

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